1. Field of the Invention
The present invention relates to a positioning control method wherein high-accuracy positioning control of a load shaft is enabled by a semi-closed loop control system in an actuator in which a wave gear drive is employed. More particularly, the invention relates to an adaptive friction compensation method making it possible to compensate for lowered positioning accuracy of a load shaft caused by variation in the frictional characteristics of a wave gear drive accompanying changes in temperature.
2. Description of the Related Art
In an actuator 2 wherein the wave gear device 1 shown in FIG. 1 is used as a reducer, it is impossible to control the positioning of a load shaft 3 of the actuator with a high degree of accuracy without accounting for variation in the frictional characteristics of the wave gear drive 1 due to temperature change. Specifically, in the actuator 2, a semi-closed loop system for controlling the position of the load shaft 3 based on the detected position of a motor shaft 6 of a motor 4 is used to perform a drive control whereby output rotation of the motor 4 is reduced via the wave gear drive 1 and transmitted from the load shaft 3 toward a load 5. Accordingly, when the friction characteristics of the wave gear drive 1 change due to changes in the ambient temperature, the accuracy with which the load shaft 3 is positioned by the semi-closed control system is lowered. In Patent Document 1 there is disclosed a servo controller for controlling the drive of an actuator, wherein a simulation is used to accurately determine the frictional force that changes with time and temperature, so that positioning control as well as other actions are performed with precision, based on the results.
JP-A 2006-146572